1. Field of the Invention
The present invention relates to a resist top coat composition and a patterning process adopting such a material, which resist top coat composition is provided for forming a top coat on a photoresist film so as to protect the photoresist film, in the field of photolithography for micro-fabrication in a manufacturing process of semiconductor device, such as liguid immersion photolithography to be achieved by adopting ArF excimer laser of 193 nm wavelength as a light source and by interposing water between a projection lens and a substrate.
2. Description of the Related Art
Recently, while finer pattern rules are demanded with highly integrated LSI's providing highly increased speeds, the light exposure technique currently used as a general one is gradually forced to encounter an inevitable limit of resolution due to wavelengths of light sources.
This fact is based on shortened wavelengths of light sources for exposure, such that wavelength shortened from i-line (365 nm) of mercury lamp down to KrF excimer laser (248 nm) has enabled mass-production of DRAM (dynamic random access memory) of 64M-bit (processing dimension of 0.25 μm or less). Further, there has been earnestly considered lithography adopting ArF excimer laser (193 nm) so as to realize production of DRAM's having integration degrees of 256M, 1G, and higher, in a manner to realize a 65 nm node device by combining the laser with a lens having a higher NA (NA≧0.9). Although utilization of F2 laser having a wavelength of 157 nm has been selected as a candidate for fabrication of 45 nm node device, its adoption has been postponed due to numerous problems such as represented by insufficient capabilities of resists in addition to demerit of cost. As such, ArF liguid immersion lithography has been proposed as an alternative of F2 lithography, and development thereof is currently being promoted toward early adoption of the former (Proc. SPIE Vol. 4690 xxix (2002)).
In the ArF liguid immersion lithography, water is impregnatedly interposed between a projection lens and a wafer, and ArF excimer laser is irradiated via water. Since water has a refractive index of 1.44 at 193 nm, patterning is enabled even with a lens having an NA of 1.0 or larger, and it is theoretically possible to increase an NA to 1.44. Resolution is improved by an increased amount of NA, to suggest a possibility of 45 nm node by a combination of a lens having an NA of 1.2 or more with ultra-high resolution technique (Proc. SPIE Vol. 5040, p 724 (2003)).
However, achievement of exposure in the presence of water on a resist film results in that acids generated within the resist film and basic compounds included in the resist material are partially caused to leach into the water layer, thereby resultingly and possibly causing pattern profile change, pattern collapse, and the like. There is also pointed out a possibility that a small amount of water droplet left on the resist film permeates into the resist film to cause defects. To overcome these drawbacks, it has been proposed in the ArF liguid immersion lithography to provide a top coat between a resist film and water (2nd Liguid immersion Work Shop: Resist and Cover Material Investigation for Liguid immersion Lithography (2003)).
It is known that top coats on photoresist films have been investigated as anti-reflection films, as represented by an ARCOR (antireflective coating on resist) method (see patent-related JP62-62520A, JP62-62521A and JP60-38821A for example). The ARCOR method is configured to form a transparent anti-reflection film on a photoresist film, and the anti-reflection film is stripped off after exposure. At that time, used as a resist top coat composition is one having a lower refractive index such as perfluoroalkyl polyethers, or perfluoroalkyl amines, in a manner to enable drastically decreased reflection light at an interface between the photoresist film and resist top coat, thereby resultingly improving dimensional accuracy. Thus, there have been proposed amorphous polymers such as perfluoro(2,2-dimethyl-1,3-dioxol)-tetrafluoroethylene copolymers as resist top coat compositions (see JP5-74700A, for example). However, these fluorine-containing compounds are low in compatibility with organic substances and require usage of flon-based solvents for coating and stripping of resist top coats, thereby leading to serious demerits from standpoints of environment and cost.
As resist top coat compositions other than the above, application of water-soluble or alkali-soluble materials have been investigated (see JP6-273926A and JP2803549, and J. Photopolymer Sci. and Technol. Vol. 18 No. 5 p. 615 (2005), for example).